Is there a reason why people come into your life?

Obviously the big relationships in your life leave a mark, and the lesson learned is crystal clear.
But perhaps every personal interaction happens for a reason.
Some people come and go like a rotating door, leaving behind a piece of wisdom or a warm memory.
Some drift in unexpectedly. And as silently as they came in, they fade out. Dissipate like early morning fog. They have left nothing — at least not that you can see.
Some enter and never leave. It is a constant exchange of knowledge and empathy, emotion and interaction, both good and bad.
And others come into your life, put down their roots, create chaos, happiness, sadness, anger — and then they’re gone, and a crater exists where your heart should be.
But why?
Why did I know that person? Why did I meet them? Why did I date them?
Why did I love them?
Was it chance … a spontaneous, unplanned meeting of two beings?
Or fate, destiny, something that was “meant to be” … like old movies and clichés would have you believe?
***
I’ve been doing a lot of thinking lately.
When I decided to write this post, I was questioning why I’d met certain people — some because the mark they left was not a positive one and others because they were special … and them leaving my life was incredibly painful.
Wouldn’t I have been better off not knowing those people?
Or is experiencing that pain, heartbreak, fear, rage, the lesson? The reason?
I wonder.